Wrap a belt around the sides of your head where you want the cut to be. If you are doing what is called a high crew cut, cut a line around the top of the belt versus the bottom. A high cut means you are bald all the way to the top of your temple. A low crew cut is bald to any point below or in the middle of your temple.
Adjust the clippers all the way forward without a guard; this is the "balding" position. If you don't want the sides of your head bald, pull the adjustment lever back completely to leave a higher shadow of hair. For thicker sides, apply the 1 guard with the lever completely back.
Cut from the bottom to the top, stopping at the edge of the belt or at the line you created using the belt. Cut with the clippers open-faced, meaning the screws are facing away. Cut over the sides twice to ensure a clean cut.
Remove the belt, and cut the top by placing the biggest guard on with the lever completely back. The amount of hair you have will determine the guard you need. Start with the biggest one and work your way down until you find the right size.
Cut evenly across the top with the chosen guard. Go over the top three or four times to get the most even results. If you are using a 4 guard, remove it and put on a 3 guard.
Cut 2 inches from the front and the back and in between those barriers. The guard will do the precision work.